Production and Quality Evaluation of Yoghurt Enriched with Two Accessions of Passion Fruits (Passiflora edulis f. flavicarpa)

Abstract

Aims: The broad objective of the research produce acceptable yoghurt flavoured with two accessions of passion fruit (pulp and skin) and evaluate its quality (physicochemical, phytochemical, microbiological, selected mineral and vitamin content). Study Design: The experimental design that was used is Completely Randomized Design. Place and Duration of Study: The study took place at the Department of Food Science and Technology, University of Nigeria, Nsukka between August 2016 and September 2017. Methodology: Yoghurt is a diary product obtained from lactic acid fermentation of milk. Yoghurt and two accessions of passion fruit juices (Passiflora edulis f. flavicarpa O. Deg) were processed to formulate enriched yoghurt in the following ratios 90:10, 80:20, 70:30, 60:40 and 50:50. Yoghurt without the passion fruit juice (100:0) served as the control. Based on sensory evaluation, the best samples were subjected to physicochemical, phytochemical, microbiological, selected mineral and vitamin content evaluation using standard methods. The best enriched yoghurt samples were those in the ratio 90:10 and 80:20. Proximate composition of the enriched yoghurt samples significantly (p<0.05) differed with the controls. Results: Enriched yoghurt showed an increase in the protein content (3.70, 3.52, 3.86, 3.93, 3.94, 3.52%) than control (2.81%). The control had higher fat content (3.43%) than enriched yoghurt (2.93, 3.12, 3.14, 2.78, 3.03 and 2.90%). The ash content ranges from 0.59 - 0.82% while addition of passion fruit juice caused pH to drop from 4.24 in the plain yoghurt to 4.18, 4.20 and 4.23 in the enriched yoghurt. The titratable acidity of yoghurt samples increased from 0.18 in the control to 0.72, 0.54, 0.52, 0.50 and 0.45 in enriched yoghurt. No direct relationship was observed between the pH and the titratable acidity. The total solid content ranges from 4.57-30.03. The phytochemicals were in trace amount. There was no significant (p>0.05) difference in the tannin content. The titratable acidity of yoghurt samples increased from 0.013 µg in the control to 0.015, 0.027, 0.028, 0.016, 0.020 and 0.024 in enriched yoghurt. Significant (p<0.05) difference in the phenolic content value was observed among all the samples. The phenolic content in the yoghurt samples ranges from 0.06 to 0.10 mg/g. The mineral content and vitamin content of the flavoured yoghurt samples significantly (p<0.05) differed with that of the control. An increase in the sodium content was observed in the samples from the control (168.24 mg/100 g) to the enriched sample (209.31, 202.66, 169.48 and 192.82 mg/100 g). Similar increases were  observed for potassium, calcium, magnesium and phosphorus content of the samples. Enriched yoghurt showed an increase in the vitamin C content (6.40, 7.53, 7.29, 7.15 and 7.13 mg/g) than in the control (5.10 mg/g). Vitamin A content ranged from 14.96 µg/100g - 20.67 µg/100 g. The total viable count was higher in the control (5.67 × 105 cfu/ml) than in enriched yoghurt. The mould count of the yoghurt samples varied from 0.33 × 101 cfu/ml - 1.58 × 103 cfu/ml. All the sensory attributes tested in the flavoured yoghurt samples significantly (p<0.05) differed. Conclusion: Yoghurt enriched with local specie passion fruit juice from pulp, was the most accepted.